I. Field
The following description relates generally to wireless communications systems and more particularly to femto cell deployments.
II. Background
Wireless communication systems or networks are widely deployed to provide various types of communication; for instance, voice and/or data may be provided through wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources. For example, a system may use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing (OFDM), and others.
Recently, users have started to replace fixed line communications with mobile communications and have increasingly demanded improved voice quality, reliable service, and low prices. In addition to mobile phone networks currently in place, a new class of small base stations has emerged, which may be installed in a user's home or other area and which provide indoor wireless coverage to mobile units using existing broadband Internet connections. Such personal miniature base stations are generally known as access point base stations, or, alternatively, Home Node B (HNB) or femto cells. Typically, such miniature base stations are connected to the Internet and the mobile operator's network through a DSL router or a cable modem.
Femto cells transmit a small amount of power and have a much smaller coverage area as compared to macro cells, which have large coverage areas. Femto cells are added in a network to provide coverage where there might be a void in the macro cell coverage and/or where extra capacity is desired. Thus, this new type of network deployment topology that includes a mixture of macro cells and femto cells is becoming more common.
Pilot PN (PseudoNoise) codes are transmitted by femto cells and/or macro cells to provide overhead information to devices that would like to gain access to sectors covered by the cells. However, there is a limit to the number of pilot PN codes that are available and, therefore, the PN codes are re-used. This is generally not a problem with macro cells, since the distance between sectors that re-use the same PN code is large. However, in a femto cell topology, the re-use frequency of the PN codes is higher and, thus, a mobile device can encounter two sectors that use the same PN code quicker than in a network that utilizes macro cells.